The above examples illustrate two issues. Keep in mind that the goal of some supporters of cardinal PR is not to satisfy a strong form of Proportionality for Solid Coalitions (PSC); but to elect one moderate centrist, and a representative for each solid coalition with a quota of supporters. This should often be an achievable goal as the number of candidates entitled to a seat under PSC is usually less than the number of seats to be filled. But by starting off with awarding a seat to the overall score winner electing a moderate is prioritized over PSC.
A second issue, seen in the second example, is that a candidate receiving only low scores can beat a candidate that is clearly entitled to a seat under PSC. This is due to a downward shift in what constitutes a neutral score as the number of seats increases. What I mean by neutral score is the minimum score that a candidate must exceed to be entitled to a seat if everyone bullet votes. This would be the corresponding score to the vote exceeded in the Droop Quota. For 0 to 5 score this would be 2.5 for a single winner election, 1 ⅔ for two winners, 1.25 for three, 1 for four, etc. For a six seat election in the above example a score of 1 isn't a low score of disapproval it's a modest score of approval.
What could be done about these issues?
1: Educate voters on strategy.
Allocated Score will achieve a proportional outcome, if all voters engage in bullet voting. Rating all candidates that the voter doesn't approve of with a score of zero is essential. The ballot options could be changed from (0, 1, 2, 3, 4, 5) to (0, 0, 0, 3, 4, 5) to stress the point. The description of STAR-PR doesn't have the top-two runoff step of STAR so there's no incentive to use intermediate scores as it is.
2: Award seats to candidates that qualify for seats based on their top scores alone first. For example: count only the ratings of 5 cast then seat the candidates that have a score of 5 times the Droop quota, following a procedure similar to the first round of PR-STV. Afterwards this would switch to Allocated Score instead of the elimination round. This should prioritize proportionality, while preserving some of the attributes of Allocated Score. Intermediary rounds could be included, counting scores of four and five and a round counting scores of three, and five in a Bucklin like manner. This would ensure that even parties that split their vote between multiple candidates would get priority over an overall score winner. There would be a confirmation process to handle surplus votes and make sure votes aren't counted twice, that would seat individual candidates sequentially, but this would fundamentally change the process from a series of single winner elections to rounds of multi-winner elections. Multiple candidates could meet the Droop quota to win the round, but the ballot deweighting process could result in not all winners being confirmed.
3: Transform the scores to adjust for the shift in the neutral point.
By adjusting the scores before they are tallied voters can score on the more familiar scale used for single winner elections and have them corrected for the distortion caused by having multiple winners.
Example: four winner election 0 to 5 ballot. The neutral score would be 1. The balance test for the equal vote criteria also changes for multi-winner. Instead of the familiar one vote canceling one vote, four votes in opposition are necessary to cancel each vote in favor(see balance test below). A score of zero remains zero, 1 becomes ⅓, 2 becomes ⅔, 3 becomes 2 ⅔, 4 becomes 3 ⅔, and 5 remains 5. Consider if four voters give a candidate a zero and one a five. Total score will be 5 and the average score will be 1. If four give a 1 and one a 4. Total score would be 4 * ⅓ + 3 ⅔ = 5 and an average of 1. If four give a score of 2 and one a 3. Total score would be 4 * ⅔ + 2 ⅓ = 5 and an average of 1. With these adjustments in place the potential harm to a preferred candidate of giving a lesser candidate an intermediate score will be on par with single winner systems.
Balance Test for Score (Based on Droop Quota rather than majority, to be applicable to any number of winners) : There shall be a set of ballots of size one plus the number of seats to be filled, such that if one of the ballots is cast any way possible the other ballots can be cast to cancel out the vote leaving the average scores for each candidate unchanged. The ballots shall be scored such that, scores of approval on one of the ballots shall be countered by the opposing score of disapproval on the other ballots, and a score of disapproval shall be countered by the opposing score of approval on one of the other ballots and the score of disapproval shall be shared with the remaining ballots.
4:Only count a fraction of the votes for each candidate.
Sequential Monroe avoids the issues by only counting the top Hare quota of ballots for each candidate. With the vast majority of low scores left uncounted, the results are largely unaffected by the distortion of scores in multi-winner elections. However, with little more than the candidates core supporters contributing, the results will lean less moderate until the final round.
What if STAR-PR was not a misleading name; and included an automatic top-two runoff based on all ballot preferences before each selection was finalized?
With the current version of Allocated Score if all voters make use of intermediate scores it will destroy any semblance of proportionality. If all voters resort to min-max voting to protect proportionality the runoff will be irrelevant. More likely voters most interested in getting a particular candidate or party elected or dead set against a particular candidate, will resort to min-max voting while voters torn between objectives will make use of the full range of scores. Vote splitting among min-max voters could result in parties failing to get a seat, and the voters making full use of all scores will have an outsized influence in getting their lesser evils elected.
Score based PR systems have the potential to provide a balance between different interests. With some of the above changes in place, parties with a quota of supporters should get one of their top two candidates elected, even if they split their votes between multiple candidates, but could end up with the one preferred by voters overall, rather than the one preferred by party members.